The present invention relates to an InP semiconductor thin film and process of fabricating the same, and more particularly a process of fabricating a semiconductor thin film comprising an InP monocrystalline layer on an Si substrate used for opto-electronic integrated circuits (OEICs), optical devices, and the like.
In a prior-art process for fabricating an InP semiconductor thin film, an InP monocrystalline thin film is formed directly on a Si substrate.
In another prior-art process, an InP buffer layer is formed on an Si substrate, and then an InP semiconductor thin film is formed on the InP buffer layer.
FIG. 2 shows an InP semiconductor thin film formed in the latter process. In the figure, reference numeral 1 denotes an Si substrate having a surface with a (100) orientation. Reference numeral 3 denotes an InP buffer layer. Reference numeral 4 denotes an InP monocrystalline layer. This InP semiconductor thin film is formed by first using reduced-pressure metal organic chemical vapor deposition (MOCVD), and triethyl-indium (TEI) and phosphine (PH.sub.3) as raw materials, to form the InP buffer layer 3 on the Si substrate 1 at a temperature of 380.degree. C., and then crystal-growing InP monocrystalline thin film 4 on the InP buffer layer 3 at 600.degree. C. As this process achieves InP crystal growth in two steps, this process is called two-step growth method. See for example Ohyobutsuri Gakkai Gakujutsu Koenkai Yokoshu (Preprints of the Symposium of the Japan Society of Applied Physics) 1986 (Autumn), page 706, No. 30p-D-6. The InP monocrystalline thin film 4 formed by the two-step crystal-growth method has an improved surface state than an InP monocrystalline thin film obtained by the single-step growth method in which an InP monocrystalline film is directly formed on an Si substrate.
However, the surface of the resultant InP semiconductor thin film obtained by the prior-art processes is not flat, nor specular (mirror-like), and the film is therefore not satisfactory for practical use. This is considered to be due to the fact that InP having a lattice constant about 8% larger than that of Si is directly crystal-grown on the Si substrate, and crystal defects due to lattice mismatch occur.